Re : Q on Back to Back Serial Interface ...

Unanswered Question
May 23rd, 2008

Hi,

I have a scenario whereby I have 2 routers that is running serial nterfaces back to back and it has nearly reached its capacity. My questions are :-

1) Here are the configuration on the routers :-

R1

--

interface Serial0/0/2

description Crossover Serial to R2 S0/0

bandwidth 1984

!

!

----------------------------------------------------------------

Serial0/0/2 is up, line protocol is up

Hardware is HWIC-Serial

MTU 1500 bytes, --> BW 1984 Kbit <-- , DLY 20000 usec,

reliability 255/255, txload 248/255, rxload 94/255

----------------------------------------------------------------

!

!

R2

--

interface Serial0/0

description 2000K cross-over to R1 S0/0/2

bandwidth 2000

load-interval 30

clockrate 2000000

end

!

!

----------------------------------------------------------------

Serial0/0 is up, line protocol is up

Hardware is PowerQUICC Serial

MTU 1500 bytes, --> BW 2000 Kbit <--, DLY 20000 usec,

reliability 255/255, txload 93/255, rxload 255/255

----------------------------------------------------------------

!

!

!

Q1 : Since this is a back-to-back serial connection, if I increase the amount on the bandwidth command to say 'bandwidth 4000' on both end of the links, would

the bandwidth on the link becomes 4MB ?

Q2 : How can I increase the bandwidth on a back-to-back serial connection ? I was thinking if I change the clockrate to 4000000, it will double the speed on the link ?

Thank you in advance,

Cheers,

- sn -

I have this problem too.
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Hi,

The bandwidth command itself has not affect on the actual bandwidth. It is used for some routing protocols (like EIGRP) to calculate metric.

The clockrate command is that what you need in this situation, but it depends on the card what is the maximum bandwith available. So please check the card specification for available maximum clockrate being supported.

If you want to achieve even higher bandwidth you can bunble multiple serial connections using MPPP.

Hope it helps, rate if does,

Krisztian

sanjaynadarajah Fri, 05/23/2008 - 00:39

Hi Kerek,

1) Thanks. Next q is that when you change the clockrate to a higher value, would you know how long will be the time for the link to come back up ? Since this is a production environment, it needs to be done when the load is low.

2) So to connect a few serials for higher bandwidth utilization, we need to use mppp ?

Thank you,

Cheers,

- sn -

Hi Sn,

1. After you change the clockrate of the interface you may experience a short outage (interface down/up) while the interface is changing the clockrate.

2. Not mppp is the only solution. It depends how do you want to implement. If you just configure another interface pair for IP u can also set up load balancing on IP level using equal metric static routes or by means of routing protocol which supports equal or non equal cost load balancing.

It really depends whether you want to achieve it on layer2 or layer3.

Please refer to this link for configuring mphttp://www.cisco.com/en/US/docs/ios/qos/configuration/guide/mlppp_over_serial.htmlpp

For layer2 aggregation the other option is the multilink frame-relay:

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/17s_mfr.html

Hope it helps, rate if does

Krisztian

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